Method and apparatus for controlling power saving mode in wireless portable internet system

ABSTRACT

Disclosed is a method and device for controlling a power saving mode for applying the sleep mode for saving power consumption to the mobility of subscriber stations in a mobile communication network and a wireless Internet system. Subscriber stations entering the sleep mode are constantly grouped, listening intervals of the subscriber stations for each group are not superimposed, the existence state of traffic in the subscriber stations is independently notified for each group, and the overhead of signaling messages is minimized when the traffic is notified to the subscriber station in the sleep mode.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a power saving mode control method anddevice in a wireless portable Internet system. More specifically, thepresent invention relates to a power saving mode control method anddevice for using a power saving mode and a sleep mode for reducing powerconsumption of mobile terminals in a mobile communication system and awireless Internet system.

(b) Description of the Related Art

A wireless portable Internet is a next generation communication schemefor further supporting mobility for short range data communicationschemes which use fixed access points, such as the conventional wirelessLAN. Various standards for the wireless portable Internet have beenproposed, and the international standard of the portable Internet hasprogressed through the IEEE 802.16e.

FIG. 1 shows a diagram of the wireless portable Internet system.

As shown, the wireless portable Internet system includes a subscriberstation (SS) 111 in cells 110 and 120, base stations 112 and 121 forperforming radio communication with the SS 111 in the cells 110 and 120,routers 131 and 132 connected to the base stations 112 and 121 through agateway, and the Internet 140. A personal computer is also provided as aterminal node 150.

The wireless LAN such as the conventional IEEE 802.11 provides a datacommunication scheme for allowing short-range wireless communicationwith reference to a stationary access point, and it does not providemobility of the SS but rather it supports the short-range datacommunication in a wireless manner instead of on the cable basis.

The wireless portable Internet system driven by the IEEE 802.16 groupguarantees mobility and provides a seamless data communication servicewhen the SS 111 shown in FIG. 1 moves to another cell from a cell.

The IEEE 802.16 basically supports the metropolitan area network (MAN),and represents an information communication network covering anintermediate area between the LAN and the WAN.

Therefore, the wireless portable Internet system supports a handover ofthe SS 111 in a like manner of the mobile communication service, andassigns dynamic Internet protocol (IP) addresses according to movementof the SS 111.

In this instance, the SS 111 communicates with the base stations 112 and121 through the orthogonal frequency division multiple access (OFDMA)system, which is a modulation and multiple access scheme having combinedthe orthogonal frequency division multiplexing (OFDM) scheme which usesthe frequency division multiple access (FDMA) scheme for using aplurality of subcarriers of orthogonal frequencies as a plurality ofsubchannels, and the time division multiple access (TDMA). The OFDMAsystem is essentially resistant to the fading phenomenon generated onthe multi-paths, and has high data rates.

Also, the IEEE 802.16 has adopted the AMC (adaptive modulation andcoding) scheme for adaptively selecting a modulation and coding schemeaccording to a request and an acceptance between the SS 111 and the basestations 112 and 121.

FIG. 2 shows a hierarchical structure of the wireless portable Internetsystem.

As shown, the hierarchical structure of the wireless portable Internetsystem of the IEEE 802.16e includes a physical layer 210 and a mediaaccess control (MAC) layer 220, and the physical layer 210 is connectedto the MAC layer 220 through a service access point (SAP).

The physical layer 210 performs radio communication functions executableon the general physical layer, such as modulation/demodulation, andcoding.

The wireless portable Internet system does not have layers classifiedaccording to their functions, but allows a single MAC layer to performvarious functions, differing from the wired Internet system.

Regarding sublayers according to functions, the MAC layer includes aprivacy sublayer 221, an MAC common part sublayer 222, and a servicespecific convergence sublayer 223.

The service specific convergence sublayer 223 performs a payload headersuppression function and a quality of service (QoS) mapping function inthe case of seamless data communication.

The MAC common part sublayer 222, which is the core part of the MAClayer, performs a system access function, a bandwidth allocationfunction, a connection establishment and maintenance function, and a QoSmanagement function.

The privacy sublayer 221 performs a device authentication function, asecurity key exchange function, and a data encryption function. Thedevice is authenticated by the privacy sublayer L21, and the user isauthenticated by an upper layer (not illustrated) of the MAC.

FIG. 3 shows a diagram of a connection configuration between a basestation (BS) and an SS in the wireless portable Internet system.

The MAC layer 220 a of the SS and the MAC layer 220 b of the BS have aconnection therebetween.

The phrase connection represents not a physically connected relation butrather a logically connected relation, and it is defined to be a mappingrelation between MAC peers of the SS and the BS in order to transmittraffic of a single service flow.

Therefore, parameters or messages defined with respect to the connectionrepresent the functions between the MAC peers, and in reality, theparameters or the messages are processed, are converted into frames, andare transmitted through the physical layers, and the frames are parsedand the functions which correspond to the parameters or the messages areexecuted on the MAC layer.

The MAC messages transmitted through the connection include: aconnection identifier (CID) which is an MAC layer address foridentifying connections; an MAP for defining a symbol offset, asubchannel offset of bursts time-divided by the SS in a downlink/uplink,a number of symbols, and a number of subchannels of allocated resources;and a channel descriptor for describing characteristics of the physicallayer according to the characteristics of the downlink/uplink (adownlink channel descriptor will be referred to as a DCD and an uplinkchannel descriptor will be referred to as a UCD hereinafter).

In addition, the MAC messages include various messages for performing arequest (REQ) function, a response (RSP) function, and anacknowledgement (ACK) function on various operations.

FIG. 4 shows a diagram for a frame structure of the wireless portableInternet system.

Referring to FIG. 4, frames include a downlink sub-frame and an uplinksub-frame depending on transmission directions. The vertical axis of theframe represents subchannel logical numbers, and the horizontal axisthereof denotes OFDMA symbol numbers.

The downlink sub-frame includes a preamble, a downlink MAP (DL-MAP), anuplink MAP (UL-MAP), and a plurality of downlink (DL) bursts. The DLbursts may not represent the channels or resources classified accordingto users, but they are classified according to transmission levels withthe same modulation scheme or channel encoding. Further, the DL burstscan be provided for respective users.

The downlink MAP has offset information, modulation method information,and coding information on a plurality of users who use the samemodulation method and channel coding, and allocates the resources to theusers. Accordingly, the MAP has a feature of broadcast channels andrequires strong robustness.

In the case of the uplink sub-frame, transmission is performed per user,and the uplink bursts have per-user information.

FIG. 5 shows a flowchart for establishing a connection process in thewireless portable Internet system.

Referring to FIG. 5, when an SS enters a base station's area in stepS501, the BS establishes downlink synchronization with the SS in stepS502. When the downlink synchronization is established, the SS acquiresan uplink parameter in step S503. For example, the parameter can beincluded in a channel descriptor message according to the physical layercharacteristics (e.g., useable burst profiles corresponding to theappropriate SNR (signal to noise ratio) levels).

A ranging process between the SS and the BS is performed in step S504.The ranging process for correcting timing, power, and frequencyinformation between the SS and the BS performs an initial rangingprocess and a periodic ranging process after the initial ranging.

When the ranging process is finished, a negotiation on basic serviceprovision capabilities for establishing connection between the SS andthe BS is performed in step S505. When the negotiation on basic serviceprovision capabilities is finished, the SS is authenticated in step S506by using a device identifier including an MAC address and a certificateof the SS.

When the authentication for the SS is finished and a usage authorizationon the wireless portable Internet is confirmed, a device address of theSS is registered in step S507, and an IP address is provided to the SSfrom an IP address management system such as a DHCP server toaccordingly establish an IP connection in step S508.

The SS assigned with the IP address performs a connection-establishmentprocess for data transmission in step S509.

The above-described wireless portable Internet system not only performscommunication near a fixed location but also has mobility in themetropolitan level differing from the conventional wireless LANcommunication systems, and hence, batteries are usually used to supplypower to the SS, and the duration of the batteries is a major limitationof the usage time in the wireless portable Internet system.

Therefore, the wireless portable Internet system such as the IEEE802.16e has proposed a sleep mode for reduction of battery powerconsumption. The sleep mode is a method for allowing a terminal to entera sleep state during a sleep window, and reduce the SS's powerconsumption when no data to be transmitted to the SS is provided. Afterentering the sleep state, the SS performs no operation for datatransmission during the sleep window, thereby saving the powerconsumption of the SS.

The SS is switched to a listening state each time the sleep window isterminated, and it checks whether data which stands by to be transmitted(to the corresponding terminal) during the sleep window are provided.

FIG. 6 shows a signal flowchart for a sleep mode operation in thewireless portable Internet system.

As shown, entering the sleep mode by the SS requires permission by theBS. The SS 111 attempting to enter the sleep mode establishes a sleepwindow to request a sleep mode from the BS 112 in step S601.

When receiving the sleep mode request, the BS assigns a sleep window totransmit a sleep mode approval to the SS in step S602.

When receiving the sleep mode approval, the SS enters the sleep mode forreceiving no data at the sleep mode entering time M in step S603. Whenthe initial sleep window is expired, the SS is switched to a listeningmode to check whether data addressed to the SS (in a transmissionstandby state) are buffered from the BS during the sleep window in stepS604.

In this instance, when no data addressed to the SS (in the transmissionstandby state) are buffered during the initial sleep window, the BS 112establishes a message for indicating existence of data traffic to be 0and transmits the same to the SS in step S605.

When it is determined that no data traffic is transmitted during thelistening mode, the SS enters the sleep mode again in step S606. In thisinstance, the sleep window can be established to be equal to or longerthan the initial sleep mode.

When data in the transmission standby state with respect to the SS 111are provided during a second sleep window, the BS can buffer the datatraffic in step S608, and existence of the buffered data are reported inthe listening mode of the SS.

The BS 112 establishes a field corresponding to the message whichindicates existence of data traffic to be a field (e.g., 1) forindicating the existence, or transmits a message which includes a listof basic CIDs which are identifiers of corresponding SSs to the SS instep S609. When receiving the message and checking that the data trafficto be transmitted to the SS 10 are found in the listening mode in stepS607, the SS 111 terminates the sleep mode, enters an awake mode toreceive the buffered data traffic, and performs data communication withthe BS 20 in step S610.

The SS 10 proceeds to the sleep mode according to the sleep modeoperation when there are no data to be transmitted, thereby preventingunnecessary power consumption.

FIGS. 7 and 8 show exemplified sleep windows in the conventional sleepmode.

FIG. 7 shows exemplified terminals operable by a power saving operationmode with a periodic sleep mode, and FIG. 8 shows a power saving modeoperation with an exponentially increasing sleep window.

Referring to FIG. 7, a subscriber station SS1 (710) listens to a frameonce for each N/4 frame, and a subscriber station SS2 (720) listens to aframe once for each N/2 frame.

Therefore, broadcast information which is needed to be listened to bythe subscriber states SS1 and SS2 is broadcast once for each N/2 frame,and information which is needed to be transmitted for a specificsubscriber station SS1 is broadcast by a subframe with a period of anN/4 frame.

However, the periodic power saving mode is easy to manage, but its powersaving efficiency is not good because most of the data traffic is shownat a specific time (i.e., a burst characteristic), and periodicswitching to the listening mode is inefficient for power saving in thedata communication system such as the Internet.

Since the data traffic other than voice traffic has a burstcharacteristic and a long-range dependence as described above, it isdesirable to exponentially increase the next sleep window when no datatraffic in the transmission standby is provided in the listening mode.

As shown in FIG. 8, a subscriber station SS3 initially has a sleepwindow of an N frame, and it exponentially increases the sleep windowsuch as to 2N, 4N, and 8N.

However, the case of exponentially increasing the sleep window iseffective when the data traffic has a long-range dependence, but itincreases complexity of the system since it must manage the sleep windowand the listening interval for the respective subscriber stations.

Also, the power saving operation method shown in FIG. 8 is not efficientfor traffic which has a very long interval and periodically appears.

As to the HIPERLAN/2 system, each SS enters the sleep state with apredetermined sleep window. In this instance, the sleep window isallowed during a frame time corresponding to a value of exponentiationof 2. The frame which corresponds to a listening interval of an SShaving a shorter sleep window is superimposed on the frame whichcorresponds to a listening interval of an SS having a longer sleepwindow. For example, the listening interval of the SS which is in thesleep mode with the period of eight frames is superimposed on thelistening interval of the SS which is in the sleep mode with the periodof four frames, which advantageously prevents repetition of managementcompared to the method of individually managing the listening intervalof each SS since the sleep windows of SSs are managed by grouping them.

However, recent transactions have reported that the Internet traffic hasa long-range dependence or self-similarity, which represents that theburst characteristic of traffic is stronger and is long-lasting.Therefore, the above-noted method is very efficient when the trafficoccurs with a fixed period, but the same may be inefficient when theself-similarity is strong in a like manner of the Internet traffic.

U.S. Pat. No. 5,758,278 (May 26, 1998) entitled “Method and apparatusfor periodically reactivating a mobile telephone system clock prior toreceiving polling signals” discloses a method which is only applicableto periodical reactivation, and finds an awaking time with less powerconsumption on the basis of periodicity to thus control the mobiletelephone to efficiently awake before periodical polling signals aregenerated.

The transaction entitled “IEEE 802.16e Sleep Mode” published in IEEE802.16e Session #24 Contribution, pp. 1 to 8 (Mar. 11, 2003) disclosesrequired improvements to be supported by the IEEE 802.16a standards inorder to support the mobility operation by reducing power consumption ofthe subscriber station. The transaction proposes a scheme for applying atypical burst characteristic of traffic, transmitting no packets in theoff period in which no packets are generated to thereby control thesubscriber station to be in the sleep mode and reduce power consumptionof the subscriber station. In particular, the scheme controls the sleepwindow to be double and reduces the power consumption of the subscriberstation when no traffic is found to be transmitted to the correspondingsubscriber station, by considering that the traffic of the Ethernet andthe Internet maintains the duration of the traffic when no traffic isprovided.

That is, the transaction applies a sleep window update algorithm whichuses an exponentially-increasing sleep window to increase the sleepwindow when no traffic is provided, thereby saving the power. However,the transaction fails to provide a method for grouping the subscriberstations and managing the grouped subscriber stations for theconventional case in which the initial sleep window has no relation tothe final sleep window, thus deteriorating the efficiency of managementand increasing the size of a signaling message.

The IEEE 802.16e system adopts a concept of exponentially increasing thesleep window in the operation of sleep mode. That is, on entering thesleep mode, the subscriber station checks the traffic during the sleepwindow, and when no traffic is found to be transmitted to the subscriberstation, the subscriber station doubles the next sleep window and entersthe sleep mode again.

The above-noted process is allowed in consideration of theself-similarity of Internet traffic, and hence, when no traffic isprovided for a predetermined period, it is more probable that no trafficis provided for a longer period, and the efficiency of the sleep mode isincreased.

In addition, the process for the subscriber station to enter the sleepmode with the initial sleep window, double the sleep window and enterthe next sleep mode when no traffic occurs during the sleep mode isrepeated until it comes to the final sleep window. The subscriberstation enters the next sleep mode with the final sleep window valuewhen the final sleep window is less than the doubled previous sleepwindow.

The above-described mechanism may generate the same effect as that ofthe sleep mode operable by the fixed sleep window when the initial sleepwindow is established to correspond to the final sleep window. However,the mechanism fails to arrange the listening intervals of the subscriberstation operable by the sleep mode, and requires searching thesubscriber stations in the sleep state for each frame in order toindicate traffic, and has a problem when a large volume of signalingmessages for indication of traffic are applied to a specific frame.

SUMMARY OF THE INVENTION

It is an advantage of the present invention to provide a power savingmode control method and device manageable by a base station andapplicable to a sleep mode operation for reducing power consumption in awireless portable Internet system.

It is another advantage of the present invention to provide a powersaving mode control method and device for minimizing overheads ofsignaling messages for traffic indication to a subscriber station in awireless portable Internet system.

In one aspect of the present invention, a system for controlling a powersaving mode of a subscriber station in a wireless portable Internetsystem comprises: a message receiver for receiving a sleep request(SLP-REQ) message from the subscriber station; a message parser forparsing the sleep request message and extracting an initial sleepwindow, a final sleep window, and a subscriber station identifier; asleep mode controller for determining an entrance time to the sleep modeby the subscriber station which requests the sleep mode according to theinitial sleep window, the final sleep window, and the subscriber stationidentifier so as to group listening intervals of a plurality ofsubscriber stations and arrange the same; a grouping database forstoring information on the sleep modes of the grouped subscriberstations and information on the groups; a sleep mode database forstoring the initial sleep windows and the final sleep windows of thegrouped subscriber stations; and a message transmitter for notifying thesleep-mode-requested subscriber station of the initial sleep windows,the final sleep windows, and the entrance time to the sleep mode.

The sleep mode controller comprises: a grouping controller forcontrolling grouping of sleep groups managed by the grouping controlleraccording to the sleep request message parsed by the message parser, andchecking which group has the least number of subscriber stations in thesleep mode from among the sleep groups; a subscriber station arrangerfor arranging the subscriber station to the group with the least numberof subscriber stations; and a sleep window determiner for determining aninitial sleep window and a final sleep window appropriate for systemmanagement, and using the initial sleep window and a final sleep windowto manage the corresponding subscriber station.

The system further comprises a frame arranger for controlling a startframe so that the grouped and arranged subscriber station may receive atraffic indication and be arranged to a frame.

The sleep mode controller parses the sleep request message, arranges thesubscriber station entering the sleep mode to the group with the leastnumber of subscriber stations, and groups the same.

The sleep mode controller determines the initial and final sleepwindows, uses the same to manage the subscriber station, and uses thesame as parameters of a sleep response message to transmit theparameters to the subscriber station.

The sleep mode controller determines the initial and final sleep windowsof the subscriber station so that listening intervals for each group maynot be superimposed.

The sleep mode controller applies notification on the traffic existencein the subscriber stations in the sleep mode to the respective groups soas to minimize the amount of information on signaling messages whenindicating the traffic to the subscriber station in the sleep mode.

The initial sleep window value is a value when the subscriber stationenters the sleep mode, and is integer-times the minimum initial sleepwindow value controlled by the base station.

The final sleep window value is a maximum window in which the subscriberstation enters the sleep state once while in the operation of sleepmode, and is integer-times the minimum initial sleep window value.

The number of sleep groups controlled by the sleep mode controller isnot greater than the minimum initial sleep window value based on thenumber of frames, and the base station assigns the subscriber station toone of sleep groups controlled by the base station.

The sleep mode controller controls a start frame so that the sleep groupto which the subscriber station is assigned may be arranged to the framefor receiving a traffic indication.

N sleep groups are controlled by the sleep mode controller, a framehaving a remainder of k (Frame_Number MOD N=k) generated by dividing thenumber of frames by N is controlled to be the start frame so as toassign a specific subscriber station to the k-th group.

In another aspect of the present invention, a method for controlling apower saving mode in a wireless portable Internet system, comprises: (a)controlling a subscriber station in the awake mode to detect that theservice provided to the subscriber station has no uplink data ordownlink data for more than a predetermined time; (b) controlling thesubscriber station to use a characteristic of the service and transmit asleep request message to which parameters are established to the basestation; (c) receiving a sleep response message including an initialsleep window, a final sleep window, and a start frame from the basestation; (d) establishing parameters for the operation of sleep modeaccording to parameters provided in the sleep response message; and (e)allowing the subscriber station to enter the sleep mode.

The initial sleep window value is a value when the subscriber stationenters the sleep mode, and is integer-times the minimum initial sleepwindow value controlled by the base station.

The final sleep window value is a maximum window in which the subscriberstation enters the sleep state once while in the operation of sleepmode, and is integer-times the minimum initial sleep window value.

The number of sleep groups is not greater than the minimum initial sleepwindow value based on the number of frames, and the base station assignsthe subscriber station to one of sleep groups controlled by the basestation.

A start frame is controlled so that the sleep group to which thesubscriber station is assigned may be arranged to the frame forreceiving a traffic indication.

In still another aspect of the present invention, a method forcontrolling a power saving mode in a wireless portable Internet systemcomprises: (a) receiving a sleep request message from a subscriberstation; (b) determining an initial sleep window and a final sleepwindow of the subscriber station; (c) using the initial sleep window andthe final sleep window and determining an entrance time to the sleepmode so as to arrange a listening interval of the sleep-mode-requestedsubscriber station and listening intervals of other subscriber stationsand group the subscriber stations; and (d) transmitting a sleep responsemessage including the initial sleep window, the final sleep window, anda start frame to the subscriber station.

In still yet another aspect of the present invention, a method forprocessing traffic indication in a power saving mode of a subscriberstation in a wireless portable Internet system comprises: (a) accessinga frame for processing traffic indication of a predetermined sleepgroup, and checking which subscriber station's sleep window is expiredfrom among the subscriber stations configuring the group; (b) checkingwhether subscriber stations have data to be transmitted; (c) controllinga base station to establish an indicator for traffic indication to thecorresponding subscriber station when the data are found in thesubscriber station; (d) transmitting a traffic indication message whenthe subscriber stations belonging to the group are checked and theindicator is established; and (e) detecting the subscriber stations tobe in the awake mode, the subscriber stations having established theindicator indicating that the subscriber stations have the data.

The method further comprises: updating the sleep window corresponding tothe subscriber station, and entering a state in which the subscriberstation is in the sleep mode when no data are found in the subscriberstation.

The indicator includes a bitmap method and an identifier list ofsubscriber stations.

According to the present invention, a large amount of traffic indicationmessages or paging messages for awaking a subscriber station whendownlink traffic is generated to the subscriber station in the sleepmode are not provided to a specific frame by establishing the number ofsubscriber stations entering the sleep mode to be constant, and inaddition, system management, system complexity, and processing loads arereduced by grouping the subscriber stations entering the sleep mode, andthe existence state of traffic to the subscriber station is notifiedwith a lesser amount of information (overloads).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention:

FIG. 1 shows a diagram of the wireless portable Internet system;

FIG. 2 shows a hierarchical structure of the wireless portable Internetsystem;

FIG. 3 shows a diagram of a connection configuration between a basestation and a subscriber station in the wireless portable Internetsystem;

FIG. 4 shows a diagram for a frame structure of the wireless portableInternet system;

FIG. 5 shows a flowchart for establishing a connection process in thewireless portable Internet system;

FIG. 6 shows a signal flowchart for a sleep mode operation in thewireless portable Internet system;

FIGS. 7 and 8 show conventional sleep windows in the sleep mode;

FIG. 9 shows a request and response process for entering a power savingmode (a sleep mode) according to an exemplary embodiment of the presentinvention;

FIG. 10 shows a method for grouping subscriber stations entering a powersaving mode (a sleep mode) according to an exemplary embodiment of thepresent invention;

FIG. 11 shows a block diagram of a power-saving mode control systemaccording to an exemplary embodiment of the present invention;

FIG. 12 shows a block diagram of a sleep mode controller of apower-saving mode control system according to an exemplary embodiment ofthe present invention;

FIG. 13 shows a flowchart of a power saving mode (a sleep mode) by asubscriber station according to an exemplary embodiment of the presentinvention;

FIG. 14 shows a flowchart of a power saving mode (a sleep mode) by abase station according to an exemplary embodiment of the presentinvention; and

FIG. 15 shows a flowchart for processing traffic indication (TRF-IND) ofa predetermined sleep mode group according to an exemplary embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, only the preferred embodiment ofthe invention has been shown and described, simply by way ofillustration of the best mode contemplated by the inventor(s) ofcarrying out the invention. As will be realized, the invention iscapable of modification in various obvious respects, all withoutdeparting from the invention. Accordingly, the drawings and descriptionare to be regarded as illustrative in nature, and not restrictive. Toclarify the present invention, parts which are not described in thespecification are omitted, and parts for which same descriptions areprovided have the same reference numerals.

With reference to drawings, a power-saving mode control method anddevice in a wireless portable Internet system according to an exemplaryembodiment of the present invention will be described.

FIG. 9 shows a request and response process for entering a power savingmode (a sleep mode) according to an exemplary embodiment of the presentinvention where time is passed in the horizontal direction.

The subscriber station (SS) transmits a sleep request (SLP-REQ) 22,message to the base station so as to enter the sleep mode. In detail,when no data are provided in the uplink and the downlink for apredetermined time frame, the subscriber station transmits a SLP-REQmessage to the base station to enter the sleep mode. The condition forentering the sleep mode is not restricted by the exemplified applicationof SLP-REQ message, and other conditions are also applicable.

Parameters of the SLP-REQ message include an initial sleep window and afinal sleep window. The subscriber station can request a desiredcondition of entrance to the sleep mode with a predetermined initialsleep window and a predetermined final sleep window from thecorresponding base station according to features of services.

When receiving the SLP-REQ message, the base station detects which grouphas the least number of subscriber stations in the sleep mode from amonga plurality of sleep groups controlled by the base station, and assignsthe corresponding subscriber station to the corresponding group.

Also, when receiving the SLP-REQ message, the base station determines aninitial sleep window and a final sleep window appropriate for systemmanagement, uses the sleep windows to manage the correspondingsubscriber station, uses the sleep windows as parameters for a sleepresponse (SLP-RSP) message, and transmits the parameters to thecorresponding subscriber station. In this instance, the base stationdetermines parameters for a sleep mode operation of the correspondingsubscriber station according to the following conditions.

1) The initial sleep window is an initial sleep window value when thecorresponding subscriber station enters the sleep mode, and allowsinteger-times the minimum initial sleep window managed by the basestation. For example, when the minimum initial sleep window is given tobe 4, the initial sleep window can be one of 4, 8, 12, . . . , 4N (N isan integer).

2) The final sleep window is a maximum sleep window when thecorresponding subscriber station enters the sleep state once in thesleep mode, and allows integer-times the minimum initial sleep windowmanaged by the base station. For example, when the minimum initial sleepwindow is given to be 4, the final sleep window can be one of 4, 8, 12,. . . , 4N (N is an integer).

3) The number of sleep groups controlled by the base station is notgreater than the minimum initial sleep window based on the number offrames, and the base station assigns a corresponding subscriber stationto one of the sleep groups and controls a start frame value so that thesleep group may be assigned to the frame for receiving a trafficindication (TRF-IND). For example, when the minimum initial sleep windowhas a value of 4, the number of sleep groups is allowed to be up to 4.

When four sleep groups G0, G1, G2, and G3 managed by the base stationare provided and the subscriber station is assigned to Group 2, it ispossible to control the number of frames at which the subscriber stationenters the sleep mode to be a predetermined number of frames whichsatisfy the condition in which the remainder generated by dividing thenumber of frames by 4 is given to be 2. That is, the number of frames atwhich the subscriber station enters the sleep mode is given to be 2, 6,. . . , 4N+2 (N is an integer). For example, when N sleep groups managedby the base station are given, it is allowed to control the frame havingthe remainder of k (Frame_Number MOD N=k) to be the start frame of thesleep mode of the subscriber station in order to allocate a specificsubscriber station to the k-th group, where the remainder of k isgenerated by dividing the number of frame by N, and the number of startframes is given to be 2.

In this case, since the base station has the number of subscriberstations belonging to the sleep groups, it is possible to assign inadvance the subscriber station which requests entrance to the sleep modeto the group with the least number of subscriber stations so that thesubscriber stations may be uniformly provided to the groups.

FIG. 10 shows a method for grouping subscriber stations entering a powersaving mode (a sleep mode) according to an exemplary embodiment of thepresent invention, illustrating that no sleep groups are superimposedwith each other when keeping the above-noted conditions 1), 2), and 3).

Referring to FIG. 10, MSS#1 is the subscriber station which has theinitial sleep window of 4 and the final sleep window of 20 and isassigned to Group 2, MSS#2 is the subscriber station which has theinitial sleep window of 8 and the final sleep window of 20 and isassigned to Group 3, and MSS#3 is the subscriber station which has theinitial sleep window of 4 and the final sleep window of 12 and isassigned to Group 1. Sleep mode parameters for the respective subscriberstations satisfy the above conditions as follows.

1) The initial sleep window value allows integer-times the minimuminitial sleep window value managed by the corresponding base station.That is, the subscriber station has the values of 4 (MSS#1 and MSS#3)and 8 (MSS#2) when the minimum initial sleep window is defined to be 4.

2) The final sleep window value allows integer-times the initial sleepwindow value. That is, the subscriber station MSS#3 has the value of 12(three times the minimum initial sleep window), and the subscriberstations MSS#1 and MSS#2 have the value of 20 (five times the minimuminitial sleep window).

3) The base station assigns a subscriber station to one of sleep groupsmanaged by the base station and controls a start frame so that the sleepgroups may be aligned to the frame for receiving a TRF-IND. That is, thestart frame number of 2 is assigned to the subscriber MSS#1 belonging toGroup 2, the start frame number of 3 is assigned to the subscriber MSS#2belonging to Group 3, and the start frame number of 1 is assigned to thesubscriber MSS#3 belonging to Group 1.

For each of the subscriber stations MSS#1, MSS#2, and MSS#3, thelistening period (i.e., a frame which has a sleep window to be expired)of the group to which the subscriber station belongs is located withinthe group to which the subscriber station belongs.

Therefore, when the subscriber stations are established to satisfy theconditions, the subscriber stations in the sleep mode respectivelyprocess the groups classified by the base station and notify thetraffic, and hence, processing loads and overheads caused by thenotification of traffic are reduced to be those of 1/(number of groups)compared to prior art having no group allocation.

FIG. 11 shows a block diagram of a power-saving mode control systemaccording to an exemplary embodiment of the present invention. Thepower-saving mode control system can be realized to a base station whichmanages subscriber stations and can apply the existing components whichcontrol the power saving mode of the wireless portable Internet system.

As shown, the power-saving mode control system includes a sleep modemessage receiver 1010, a message parser 1020, a subscriber stationidentifier 1030, a sleep mode controller 1040, a traffic receiver 1050,a grouping database 1060, a sleep window database 1070, and a sleep modemessage transmitter 1080.

The sleep mode message receiver 1010 receives a SLP-REQ from asubscriber station.

The message parser 1020 parses the SLP-REQ, extracts a subscriberstation identifier, an initial sleep window, and a final sleep windowtherefrom, and transmits the same to the sleep mode controller 1040 andthe subscriber station identifier 1030.

The sleep mode controller 1040 controls grouping of the sleep groupsmanaged by the sleep mode controller 1040 according to the SLP-REQparsed by the message parser 1020, and in this instance, the subscriberstation which has requested the entrance to the sleep mode can beassigned to the group with a lesser number of subscriber stations inadvance. Also, the sleep mode controller 1040 uses the subscriberstation identifier, the initial sleep window, and the final sleep windowto control the subscriber station's entrance time to the sleep mode.

The sleep window database 1070 stores information on the initial sleepwindows and the final sleep windows for the respective subscriberstations.

When the subscriber station is grouped together with other subscriberstations according to the control of entrance time to the sleep mode,the grouping information is stored in the grouping database 1060 and isupdated according to a sleep mode request by the subscriber station.

When the entrance time to the sleep mode is determined by the sleep modecontroller 1040, the sleep mode message transmitter 1080 transmits amedium access control (MAC) message (e.g., an SLP-RSP) including theinitial sleep window, the final sleep windows, and the entrance time tothe sleep mode to the subscriber station in response to the sleep moderequest.

The traffic receiver 1050 receives traffic information through theInternet, and establishes an indicator for traffic indication to thesubscriber station so that the sleep mode controller 1040 may switch thesubscriber station having entered the sleep mode into the awake mode,and the traffic receiver 1050 also transmits the TRF-IND message to thesubscriber station through a traffic transmitter (not illustrated).

FIG. 12 shows a block diagram of a sleep mode controller of apower-saving mode control system according to an exemplary embodiment ofthe present invention.

As shown, the sleep mode controller includes a grouping controller 1041,a subscriber station assigner 1042, a sleep window determiner 1043, anda frame arranger 1044.

The grouping controller 1041 controls grouping of the sleep groupsmanaged by the grouping controller 1041 according to the SLP-REQ messageparsed by the message parser 1020, and identifies the subscriber stationparsed by the subscriber station identifier 1030.

The subscriber station assigner 1042 assigns a subscriber station to thegroup with a lesser number of subscriber stations in advance inconsideration of the number of subscriber stations, and stores theassignment data in the grouping database 1060.

In detail, the message parser 1020 parses the SLP-REQ message, extractsa subscriber station identifier, an initial sleep window, and a finalsleep window therefrom, and provides the same to the grouping controller1041, and the grouping controller 1041 checks which group has the leastnumber of subscriber stations in the sleep mode from among the sleepgroups managed by the grouping controller 1041, and the subscriberstation assigner 1042 assigns the corresponding subscriber station tothe checked group.

The sleep window determiner 1043 determines the initial and final sleepwindows appropriate for system management, uses the same to themanagement of the corresponding subscriber station, stores the same inthe sleep window database 1070, and transmits the same to the subscriberstation as parameters of the SLP-RSP message.

The frame arranger 1044 controls the start frame so that the subscriberstation of the designated sleep group may receive the TRF-IND and bearranged to the frame.

FIG. 13 shows an operational flowchart of a power saving mode (a sleepmode) by a subscriber station according to an exemplary embodiment ofthe present invention.

Referring to FIG. 13, a process for a normal entrance to the sleep modeexcluding an exceptional case such as rejection of entrance is shown.

The subscriber station is in the awake state in step S1201.

When the subscriber station detects no uplink or downlink data in theservice provided to the subscriber station for more than a predeterminedtime Tset in step S1202, the subscriber station uses the characteristicof the service, transmits an SLP-REQ message with established parametersto the base station in step S1203, and stands by for an SLP-RSP messagein step S1204.

When receiving the SLP-RSP message in step S1205, the subscriber stationestablishes parameters for sleep mode operation according to theparameters designated in the SLP-RSP message in step S1206, and entersthe sleep mode in step S1207. In this instance, the parametersdesignated in the SLP-RSP message include an initial sleep window and afinal sleep window determined by the above-described conditions 1), 2),and 3). Therefore, when a start frame is established, the sleep windowincreases to the final sleep window from the initial sleep window, andthe final sleep window state is then maintained.

FIG. 14 shows a flowchart of a power saving mode (a sleep mode) by abase station according to an exemplary embodiment of the presentinvention. In this instance, the process of normal entrance to the sleepmode is exemplified, and no exceptional case will be described.

Referring to FIG. 14, the base station detects that a predeterminedsubscriber station is in the BS-SS awake mode in step S1301. Whenreceiving an SLP-REQ message from the subscriber station while in theawake mode in step S1302, the base station uses the number of subscriberstations configuring the sleep groups managed by the base station, andassigns a sleep group for the subscriber station in step S1303. Forexample, when four groups are provided such that Group 0 has 32subscriber stations, Group 1 has 30 subscriber stations, Group 2 has 25subscriber stations, and Group 3 has 31 subscriber stations, the basestation assigns the sleep group of the subscriber station to Group 2.

The base station transmits an SLP-RSP message to the correspondingsubscriber station in step S1304, and enters a BS-SS sleep mode in stepS1305, and the parameters of the SLP-RSP message are determinedaccording to the three conditions.

As described above, 1) the initial sleep window value allowsinteger-times the minimum initial sleep window value managed by the basestation, 2) the final sleep window value allows integer-times theminimum initial sleep window value, and 3) the number of sleep groupsmanaged by the base station is established to be not greater than theframe-based minimum initial sleep window value, the base station assignsthe subscriber station to one of sleep groups controlled by the basestation and controls the start frame so that the sleep group to whichthe subscriber station is designated may be arranged to the frame whichreceives the TRF-IND as previously shown in FIG. 10.

FIG. 15 shows a flowchart for processing traffic indication (TRF-IND) ofa predetermined sleep mode group according to an exemplary embodiment ofthe present invention.

Referring to FIG. 15, when the base station reaches the frame in whichthe base station processes the TRF-IND of a specific sleep group in stepS1401, for example, when the base station reaches the frame number of 0(i.e., Group 0) which is the remainder generated by dividing the framenumbers by 4, the base station checks the sleep window of whichsubscriber station is expired from among the subscribers configuring thegroup in step S1402. In this instance, no processing time is considered.

The base station checks whether data to be transmitted to the subscriberstation are provided in step S1403, and when no data to be transmittedthereto are found, the base station updates the sleep windowcorresponding to the subscriber station in step S1407, and enters theBS-SS sleep mode in step S1401.

When the data are found, the base station establishes an indicator fortraffic indication to the subscriber station in step S1404, and theindicator includes the bitmap method and the method of having anidentifier list of subscriber stations.

When the subscriber stations belonging to the group are checked and theindicator is established, the base station transmits a TRF-IND messageto the subscriber station in step S1405, and the subscriber stationswith the indicator indicating the existence of data enter the awake modein step S1406.

Accordingly, the base station and the subscriber stations can operateand process the sleep mode and notify traffic with the minimizedoverheads.

The subscriber stations entering the sleep mode are grouped, the numberof subscriber stations belonging to each group becomes constant, thelistening intervals of subscriber stations for each group are notsuperimposed, and hence, the overheads of notification signalingmessages on the existence of traffic in the subscriber station in thesleep mode are reduced to 1/(number of groups) overheads compared to theconventional ungrouping method.

In addition, notification of traffic existence in the subscriber stationin the sleep mode is independently applicable to each group, and theoverheads of signaling messages are minimized when notifying the trafficof the subscriber station in the sleep mode.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

1. A system for controlling a power saving mode of a subscriber station in a wireless portable Internet system, the system comprising: a message receiver for receiving a sleep request message from the subscriber station; a message parser for parsing the sleep request message and extracting an initial sleep window that is an initial sleep window value when the subscriber station enters a sleep mode, a final sleep window that is a maximum sleep window when the subscriber station enters the sleep mode, and a subscriber station identifier; a sleep mode controller for determining an entrance time to the sleep mode by the subscriber station which requests the sleep mode according to the initial sleep window, the final sleep window, and the subscriber station identifier for group listening intervals of a plurality of subscriber stations; a grouping database for storing information on sleep modes of the grouped subscriber stations and information on the grouped subscriber stations; a sleep mode database for storing initial sleep windows and final sleep windows of the grouped subscriber stations; and a message transmitter for notifying the sleep-mode-requested subscriber station of the initial sleep windows, the final sleep windows, and the entrance time to the sleep mode.
 2. The system of claim 1, wherein the sleep mode controller comprises: a grouping controller for controlling grouping of sleep groups managed by the grouping controller according to the sleep request message parsed by the message parser, and checking which group has the least number of subscriber stations in the sleep mode from among the sleep groups; a subscriber station arranger for arranging the subscriber station to the group with the least number of subscriber stations; and a sleep window determiner for determining an initial sleep window and a final sleep window appropriate for system management, and using the initial sleep window and a final sleep window to manage the corresponding subscriber station.
 3. The system of claim 1, further comprising a frame arranger for controlling a start frame so that the grouped and arranged subscriber stations may receive a traffic indication and be arranged to a frame.
 4. The system of claim 1, wherein the sleep mode controller parses the sleep request message, arranges the subscriber station entering the sleep mode to the group with the least number of subscriber stations, and groups the same.
 5. The system of claim 1, wherein the sleep mode controller determines the initial and final sleep windows, uses the same to manage the subscriber station, and uses the same as parameters of a sleep response message to transmit the parameters to the subscriber station.
 6. The system of claim 1, wherein the sleep mode controller determines the initial and final sleep windows of the subscriber station so that listening intervals for each group may not be superimposed.
 7. The system of claim 1, wherein the sleep mode controller applies notification on the traffic existence in the subscriber stations in the sleep mode to the respective groups so as to minimize the amount of information on signaling messages when indicating the traffic to the subscriber station in the sleep mode.
 8. The system of claim 1, wherein the initial sleep window value is a value when the subscriber station enters the sleep mode, and is integer-times the minimum initial sleep window value controlled by the base station.
 9. The system of claim 1, wherein the final sleep window value is the maximum window in which the subscriber station enters the sleep state once while in the operation of sleep mode, and is integer-times the minimum initial sleep window value.
 10. The system of claim 1, wherein the number of sleep groups controlled by the sleep mode controller is not greater than the minimum initial sleep window value based on the number of frames, and the base station assigns the subscriber station to one of sleep groups controlled by the base station.
 11. The system of claim 10, wherein the sleep mode controller controls a start frame so that the sleep group to which the subscriber station is assigned may be arranged to the frame for receiving a traffic indication.
 12. The system of claim 11, wherein when N sleep groups are controlled by the sleep mode controller, a frame having a remainder of k (Frame_Number MOD N=k) generated by dividing the number of frames by N is controlled to be the start frame so as to assign a specific subscriber station to the k-th group.
 13. A method for controlling a power saving mode in a wireless portable Internet system, the method comprising: (a) controlling a subscriber station in an awake mode to detect that a service provided to the subscriber station has no uplink data or downlink data for more than a predetermined time; (b) controlling the subscriber station to use a characteristic of the service and transmit a sleep request message to which parameters are established to a base station; (c) receiving a sleep response message including an initial sleep window that is an initial sleep window value when the subscriber station enters a sleep mode, a final sleep window that is a maximum sleep window when the subscriber station enters the sleep mode, and a start frame from the base station; (d) establishing parameters for sleep mode operation according to parameters provided in the sleep response message; and (e) allowing the subscriber station to enter the sleep mode.
 14. The method of claim 13, wherein the initial sleep window value is a value when the subscriber station enters the sleep mode, and is integer-times the minimum initial sleep window value controlled by the base station.
 15. The method of claim 13, wherein the final sleep window value is the maximum window in which the subscriber station enters the sleep state once while in the operation of sleep mode, and is integer-times the minimum initial sleep window value.
 16. The method of claim 13, wherein the number of sleep groups is not greater than the minimum initial sleep window value based on the number of frames, and the base station assigns the subscriber station to one of sleep groups controlled by the base station.
 17. The method of claim 16, wherein a start frame is controlled so that the sleep group to which the subscriber station is assigned may be arranged to the frame for receiving a traffic indication.
 18. A method for controlling a power saving mode in a wireless portable Internet system, the method comprising: (a) receiving a sleep request message from a subscriber station; (b) determining an initial sleep window that is an initial sleep window value when the subscriber station enters a sleep mode and a final sleep window that is a maximum sleep window when the subscriber station enters the sleep mode of the subscriber station; (c) using the initial sleep window and the final sleep window and determining an entrance time to the sleep mode so as to arrange a listening interval of the sleep-mode-requested subscriber station and listening intervals of other subscriber stations and group the subscriber stations; and (d) transmitting a sleep response message including the initial sleep window, the final sleep window, and a start frame to the subscriber station.
 19. A method for processing traffic indication in a power saving mode of a subscriber station in a wireless portable Internet system, the method comprising: (a) reaching a frame for processing traffic indication of a predetermined sleep group, and checking which subscriber station's sleep window is expired from among the subscriber stations configuring the predetermined sleep group; (b) checking whether corresponding subscriber stations have data to be transmitted; (c) controlling a base station to establish an indicator for traffic indication to the corresponding subscriber station when the data are found in the subscriber station; (d) transmitting a traffic indication message when the subscriber stations belonging to the group are checked and the indicator is established; and (e) detecting the subscriber stations to be in the awake mode, the subscriber stations having established the indicator indicating that the subscriber stations have the data.
 20. The method of claim 19, further comprising: updating the sleep window corresponding to the subscriber station, and entering a state in which the subscriber station is in the sleep mode when no data are found in the subscriber station.
 21. The method of claim 19, wherein the indicator includes a bitmap method and an identifier list of subscriber stations. 